1. Field of the Invention
The invention relates to the field of ophthalmology, in particular to the field of optical treatment of an eye""s fundus using lasers. More specifically it deals with the application of computer based image generation, processing and central control means to accurately treat sites on an eye""s retina, particularly its macula in connection with diode laser sources and optical fibers.
2. Information Disclosure Statement
Laser methods are widely accepted in today""s modern ophthalmology, as well as in pure diagnosis like laser scanning ophthalmoscopes for the treatment of an eye. Treatment methods include laser reshaping of the cornea to correct strong myopic or presbyopic effects, laser surgery in the eye itself and several treatments of the retina. Retina related methods include coagulation laser systems and, more recently, PhotoDynamic Therapy (PDT) treatments of the retina. For example coagulation laser treatment can be used to re-weld the retina to the eye background if the retina tends to loosen from the eye background, which can lead to complete blindness. Another kind of therapy is to stop the so called age related macula degeneration (AMD). This disease is characterized by untypical blood agglomeration in the macula, the part of highest vision sensitivity of the retina. These blood agglomerations do still circulate, hence it is possible to make an accurate diagnosis applying the so called fluorescence angiography. A certain fluorescing drug is added to the patient""s blood circuit and then an image of the retina is taken. The fluorescing drug allows the exact visualization of all blood vessels on the retina and thus in particular those being responsible for the age related macula degeneration. This degeneration actually can not be reversed, but it can be stopped hence the complete loss of eyesight can be prevented.
A recent method is based on so called PDT means. In this treatment, a PDT drug is introduced into the patients blood circulation. The drug is originally harmless and has usually no therapeutic effects, but it is sensitive to illumination at a certain wavelength. If light of this suitable wavelength is absorbed by the drug molecules, they undergo a chemical reaction to another product, which is responsible for the therapeutic effect. In a simple case, this effect is the excitation of the drug molecule to an excited state where it can react with oxygen to form singlet oxygen which is highly reactive. The singlet oxygen quickly reacts with nearby tissue to oxidize it, i.e. cause necrosis. Alternatively, the splitting of one molecule can create two radicals, which are chemically very reactive and can destroy body cells. Because this method is very selective, it widely prevents negative side effects of the therapy by only illuminating the infected area. Typical applications apart from the therapy of the age related macula include tumor treatments, are catheter disinfection and dermatological applications. Concerning the treatment of age related macula degeneration, recently the described simple PDT method has been applied. The drug was given to the patient and after a certain time the macula was illuminated with the beam spot of light at the critical wavelength, preferably provided by a laser or a fiber coupled diode laser. Blood agglomeration vessels are then destroyed by the generated therapeutic substance and the age related macula degeneration is stopped. In U.S. Pat. No. 5,336,216 [D. A. Dewey ] a method for generating a treatment beam spot on the retina is claimed, which in particular generates a spot on the retina which has a rectangular intensity profile, also known as top-hat profile for all sizes. This method suffers from the fact, that the knowledge about the treatment zone is only rudimentary.
As described in the latter the treatment can be significantly enhanced if the treatment zone is well known.
As noted above, laser based methods of fundus treatment is widely accepted in today""s ophthalmology and applied in different forms. For several forms of the treatments focused laser beams are used, as for example in laser abrasive cornea treatment in order to correct myopic or presbyopic defects. Further, laser coagulation routines are performed, in order to re-weld the retina to the eye background, if it becomes unbound, which would result in complete blindness. PDT treatment is a relatively novel method to heal certain diseases of the eye. Especially successful it can be used for the correction of the so called AMD, where certain defects of the blood vessels in the macula can cause the macula to loose from the eye background. The photodynamic substances are introduced to the patients blood circuit and the treatment zone is irradiated with light of a suitable wavelength in order to start a localized treatment effect only in the region of the treatment zone. Several disadvantages are associated with the state of the art in today""s PDT methods. The most striking is the strong inaccuracy of the process can be attributed to the lack of means for an accurate determination of the treatment zone and therefore the lack of beam area generating devices providing the desired accuracy.
However, the state of the art illumination means are designed such, that it is impossible to obtain an illumination of the treatment zone alone. The operator has to calculate from fluorescence angiographic diagnostics how large the treatment area is, and then manually adjust the laser beam spot size to be large enough to completely cover the treatment area. This method is extremely inaccurate since no information about the specific eye is provided therein. The spot size on the retina varies with different patient""s different eyeballs, but the justification is absolute. This problem is addressed by the present invention.
Since the typically used slit-lamp generated pictures are only of medium quality the treatment zone can be hardly noticeable therein. Hence it""s size must be determined from the fluorescence angiography, but this image does not have any relation to the images generated by the slit lamp, though it is the same eyeball, for reasons of different optics, different viewing angles and so on. In any case, whether the treatment is determined from the slit lamp picture or from the angiography, the error made by the calculation of the beam spot size is significant and typically exceeds 200%.
For this reason it is obvious, that not only the treatment zone is illuminated, but also the healthy zones in the eye. This can lead to the destruction of important blood vessels followed by a reduction of eyesight. The present invention provides a solution to this.
State of the art methods apply a treatment beam source which generates a round intensity profile, this intensity profile is either of a gaussian or near gaussian shape or of a so called top hat structure which is characterized by a very sharp edged rise and fall of the intensity at the edges and a near constant intensity in the middle. In any case, the created variable spot size is of a round shape. Obviously, the shape of the treatment zone is not necessarily round. In the most simple case, it has an oval or a slit form but typically the shape of the area needing treatment is of a more complicated structure. Since, in state of the art devices and methods to perform fundus treatments, there is a very large error in treatment areas anyway, there has been no need for generating a better overlap of the treatment zone and the treatment beam spot area. This is addressed in the present invention now that the treatment beam is more accurately formed and projected onto the treatment zone.
A general problem in laser based fundus treatment is the movement of the eyeball during the treatment. From clinical studies the optimal illumination times are known, but during treatment it must be assured that the treatment zone is illuminated for this period. State of the art solutions operated with an real time viewing by the operator by means of a fundus viewing ocular. The device further provides means for the operator to switch the treatment beam source on an off and thus to control the beam source such, that the illumination is only working, if the treatment zone is within a certain region. This method is a potential source of inaccuracy, because both, the beam and the treatment zone are barely visible during the treatment. The present invention provides a solution to this and the several problems identified above.
It is an object of the invention to provide a method of accurately adjusting the laser beam spot size to the treatment area for each specific eyeball.
It is another object of the invention to determine the exactly the size of the treatment zone from a digital processing of angiography and slit lamp image.
It is yet another object of the invention, to provide an device to achieve significantly better overlap of the treatment zone and the treatment beam spot area.
It is further an object of the invention to provide an device allowing an accurate viewing and means for automatic switching of the beam source depending on the eye movement as well as a device capable of adjusting the spot area in real time according to the eye movement.
Briefly stated, the present invention provides a system and method to accurately treat sites on an eye""s retina employing computer based image generation, processing and central control means in conjunction with diode laser sources and optical fibers. The system and method accurately determine geometry of a treatment zone of a specific eye""s fundus and adjust a treatment beam to irradiate the treatment zone with minimal coverage of adjacent well tissue. The treatment zone or zone is accurately determined with digital processing of angiographic data and slit lamp image data. This information is integrated with information on the treatment beam characteristics to better match treatment beam coverage with minimal overlap with healthy areas of the fundus. Additionally preferred embodiments also have the ability to automatically track eye movement and switch the beam source depending on eye movement, adjusting the beam spot area in real time.
The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numbers in different drawings denote like items.